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TreeExplorer: document arcane special case

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...which happens to be supported out of the box,
due to the generic adaptor magic shared with the explore-operation

Exploiting this feature, some functor could even subvert the layering order
This commit is contained in:
Fischlurch 2017-12-03 06:25:13 +01:00
parent ca270028a9
commit 823848db37
2 changed files with 74 additions and 29 deletions
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37
tests/library/iter-tree-explorer-test.cpp
View file

@ -88,11 +88,10 @@ namespace test{
* This iteration _"state core" type_ describes
* a descending sequence of numbers yet to be delivered.
*/
class CountDown
struct CountDown
{
uint p,e;
public:
CountDown(uint start =0, uint end =0)
: p(start)
, e(end)
@ -444,14 +443,20 @@ namespace test{
* and the resulting entity is again a Lumiera Forward Iterator with suitable value type.
* The transformation function is invoked only once per step and the result produced by
* this invocation is placed into a holder buffer embedded within the iterator.
* @note since the implementation uses the same generic adaptor framework,
* the transformation functor may be defined with the same variations
* as described for the expand-operation above. In theory, it might
* collaborate with the embedded "state core" type, thereby possibly
* bypassing other decorators added below.
* @warning don't try this at home
*/
void
verify_transformOperation()
{
auto multiply = [](int v){ return 2*v; };
auto multiply = [](int v){ return 2*v; }; // functional map: value -> value
_Fmt embrace{"≺%s≻"};
auto formatify = [&](auto it){ return string{embrace % *it}; };
auto formatify = [&](auto it){ return string{embrace % *it}; }; // generic lambda: assumed to take an Iterator&
auto ii = treeExplore (CountDown{7,4})
@ -469,6 +474,8 @@ namespace test{
VERIFY_ERROR (ITER_EXHAUST, ++ii );
// demonstrate chaining of several transformation layers
vector<int64_t> numz{1,-2,3,-5,8,-13};
CHECK ("≺1≻-≺-2≻-≺3≻-≺-5≻-≺8≻-≺-13≻" == materialise (treeExplore(numz)
@ -527,6 +534,28 @@ namespace test{
VERIFY_ERROR (ITER_EXHAUST, *ii );
CHECK (fact == 2*23); // exhaustion detected on source and thus no further evaluation
// demonstrate a transformer accessing the source state core...
// should not be relevant in practice, but works due to the generic adapters
auto kk = treeExplore(CountDown{9,4})
.transform([](CountDown& core)
{
uint delta = core.p - core.e;
if (delta % 2 == 0)
--core.p; // EVIL EVIL
return delta;
});
CHECK (5 == *kk); // the delta between 9 (start) and 4 (end)
++kk;
CHECK (4 == *kk); // Core manipulated by SIDE-EFFECT at this point...
CHECK (4 == *kk); // ...but not yet obvious, since the result is cached
++kk;
CHECK (2 == *kk); // Surprise -- someone ate my numberz...
++kk;
CHECK (isnil (kk));
}

66
wiki/thinkPad.ichthyo.mm
View file

@ -5092,11 +5092,16 @@
<node CREATED="1510941397907" ID="ID_993148577" MODIFIED="1510941406366" TEXT="zun&#xe4;chst als abstrakter Baustein"/>
<node CREATED="1510941406978" ID="ID_1048232110" MODIFIED="1510941437002" TEXT="sp&#xe4;ter mit IterExplorer verschmelzen"/>
</node>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1510941455667" ID="ID_1945607867" MODIFIED="1510941522371" TEXT="Builder">
<icon BUILTIN="flag-yellow"/>
<node COLOR="#338800" CREATED="1510941455667" ID="ID_1945607867" MODIFIED="1512278476654" TEXT="Builder">
<icon BUILTIN="button_ok"/>
<node CREATED="1511054840038" ID="ID_18464349" MODIFIED="1511054851543" TEXT="brauch ich am Ende &#xfc;berhaupt einen builder">
<icon BUILTIN="help"/>
</node>
<node CREATED="1512278433500" ID="ID_1806674229" MODIFIED="1512278469093" TEXT="TreeExplorer fungiert als Builder">
<icon BUILTIN="yes"/>
<node CREATED="1512278445042" ID="ID_205794467" MODIFIED="1512278456012" TEXT="wird jeweils on top dar&#xfc;bergebaut"/>
<node CREATED="1512278456672" ID="ID_488770369" MODIFIED="1512278462388" TEXT="wird in jedem Schritt gestrippt"/>
</node>
</node>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1510941463562" ID="ID_845080696" MODIFIED="1510941523082" TEXT="TreeExplorer">
<icon BUILTIN="flag-yellow"/>
@ -5322,8 +5327,8 @@
</node>
</node>
</node>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511827103749" ID="ID_1699316886" MODIFIED="1511837183001" TEXT="transform-Operation">
<icon BUILTIN="pencil"/>
<node COLOR="#338800" CREATED="1511827103749" ID="ID_1699316886" MODIFIED="1512278362994" TEXT="transform-Operation">
<icon BUILTIN="button_ok"/>
<node CREATED="1511827249561" ID="ID_794510302" MODIFIED="1511827265634" TEXT="strikt nach Dekorator-Pattern"/>
<node CREATED="1511827337686" ID="ID_1214119488" MODIFIED="1511827345695" TEXT="bestehendern TransformIter verwenden?">
<node CREATED="1511827584523" ID="ID_1921395634" MODIFIED="1511827600541" TEXT="nein: wir m&#xfc;ssen von der Core erben">
@ -5408,10 +5413,11 @@
</node>
</node>
</node>
<node CREATED="1511918986936" ID="ID_667088953" MODIFIED="1511918989357" TEXT="Konstrukt">
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511919003054" ID="ID_1728459315" MODIFIED="1511919013829" TEXT="Aufsetz-Punkt">
<icon BUILTIN="flag-yellow"/>
<node COLOR="#338800" CREATED="1511919032171" ID="ID_737737817" MODIFIED="1512010665827" TEXT="Problem Parent::Iterator">
<node COLOR="#338800" CREATED="1511918986936" ID="ID_667088953" MODIFIED="1512278389194" TEXT="Konstrukt">
<icon BUILTIN="button_ok"/>
<node COLOR="#338800" CREATED="1511919003054" ID="ID_1728459315" MODIFIED="1512278353753" TEXT="Aufsetz-Punkt">
<icon BUILTIN="button_ok"/>
<node COLOR="#338800" CREATED="1511919032171" FOLDED="true" ID="ID_737737817" MODIFIED="1512278392539" TEXT="Problem Parent::Iterator">
<icon BUILTIN="button_ok"/>
<node CREATED="1511919050960" ID="ID_1621131204" MODIFIED="1512256810082" TEXT="grunds&#xe4;tzliches Problem jedes Iterator-Dekorators">
<richcontent TYPE="NOTE"><html>
@ -5463,9 +5469,11 @@
<node CREATED="1512010371291" ID="ID_563900951" MODIFIED="1512010383805" TEXT="bietet die ExtensionPoints einer State-Core"/>
</node>
</node>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511837027405" ID="ID_233806852" MODIFIED="1511837172811" TEXT="Argument-Detektor-Magie">
<icon BUILTIN="flag-yellow"/>
<node CREATED="1511837039180" ID="ID_1296099637" MODIFIED="1511837047198" TEXT="ganz analog zur expand-Operation"/>
<node COLOR="#338800" CREATED="1511837027405" ID="ID_233806852" MODIFIED="1512278360077" TEXT="Argument-Detektor-Magie">
<icon BUILTIN="button_ok"/>
<node CREATED="1511837039180" ID="ID_1296099637" MODIFIED="1512278401909" TEXT="ganz analog zur expand-Operation">
<icon BUILTIN="idea"/>
</node>
<node CREATED="1511837047810" ID="ID_684902103" MODIFIED="1511837057125" TEXT="kann man die Traits wiederverwenden?">
<node CREATED="1512179380102" ID="ID_657845891" MODIFIED="1512179382618" TEXT="schaut gut aus"/>
<node CREATED="1512182255367" ID="ID_1818058437" MODIFIED="1512182259778" TEXT="Funktor-Argument">
@ -5770,23 +5778,14 @@
</node>
</node>
</node>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1510969031379" ID="ID_358406634" MODIFIED="1511835528239" TEXT="verify_transformOperation();">
<icon BUILTIN="pencil"/>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511835550655" ID="ID_1305788204" MODIFIED="1511835762571" TEXT="Transformer(Iter&lt;Core&gt;)">
<icon BUILTIN="flag-yellow"/>
<node COLOR="#338800" CREATED="1510969031379" ID="ID_358406634" MODIFIED="1512278328452" TEXT="verify_transformOperation();">
<icon BUILTIN="button_ok"/>
<node COLOR="#338800" CREATED="1511835550655" ID="ID_1305788204" MODIFIED="1512276390701" TEXT="Transformer(Iter&lt;Core&gt;)">
<icon BUILTIN="button_ok"/>
</node>
<node COLOR="#338800" CREATED="1511835603751" ID="ID_6147833" MODIFIED="1512276267722" TEXT="Transformer(Iter&lt;Val&gt;)">
<icon BUILTIN="button_ok"/>
</node>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511835572331" ID="ID_90684440" MODIFIED="1511835751909" TEXT="Transformer(Core)">
<icon BUILTIN="flag-yellow"/>
<node CREATED="1511835638915" ID="ID_678182318" MODIFIED="1512276256127" TEXT="nicht m&#xf6;glich direkt auf TreeExplorer"/>
<node CREATED="1511835650761" ID="ID_1585618081" MODIFIED="1511835751909" TEXT="aber chained Transform sollte so funktionieren"/>
<node BACKGROUND_COLOR="#fdfdcf" COLOR="#ff0000" CREATED="1511835667743" ID="ID_1089942674" MODIFIED="1511835751909" TEXT="Typ verifizieren!">
<font NAME="SansSerif" SIZE="10"/>
<icon BUILTIN="flag-pink"/>
</node>
</node>
<node COLOR="#338800" CREATED="1511835716176" ID="ID_1407397782" MODIFIED="1512276211354" TEXT="Transformer mit Seiteneffekt">
<icon BUILTIN="button_ok"/>
</node>
@ -5870,8 +5869,25 @@
<icon BUILTIN="button_ok"/>
</node>
</node>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511835901999" ID="ID_1717235881" MODIFIED="1511836238870" TEXT="Transform: Core&amp; -&gt; irgendwas">
<node CREATED="1511835901999" ID="ID_1717235881" MODIFIED="1512278299862" TEXT="Transform: Core&amp; -&gt; irgendwas">
<icon BUILTIN="help"/>
<node CREATED="1512276512313" ID="ID_725756500" MODIFIED="1512276517860" TEXT="sollte theoretisch m&#xf6;glich sein"/>
<node CREATED="1512276524111" ID="ID_453994757" MODIFIED="1512276583587" TEXT="nicht sonderlich sinnvoll">
<richcontent TYPE="NOTE"><html>
<head>
</head>
<body>
<p>
...weil man den konkreten Typ der Core kennen mu&#223;
</p>
</body>
</html>
</richcontent>
</node>
<node COLOR="#338800" CREATED="1512276518472" ID="ID_1860559214" MODIFIED="1512278316412" TEXT="per Testfall dokumentiert">
<icon BUILTIN="button_ok"/>
</node>
</node>
</node>
<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1510969031379" ID="ID_722056043" MODIFIED="1511227804622" TEXT="verify_combinedExpandTransform();">